1. Field of the Invention
The present invention relates to particulate hydroperoxidized poly-N-vinyl lactam, a method of preparing the same, and the use thereof in the preparation of graft copolymers with at least one hydrophobic monomer or hydrophilic monomer, and optionally a crosslinking agent. The resulting copolymers possess unexpectedly low extractibles and good mechanical properties and are useful in various biomedical applications, including contact lenses, medical surgical devices such as heart valves, vessel substitutes, mouth guards and denture liners, as semipermeable membranes, and as films or fibers, e.g. for textile uses or as burn and wound dressings.
2. Prior Art
Polyvinyl pyrrolidone and its use in the preparation of graft or block copolymers with hydroxyethyl methacrylate finding applications for a variety of purposes, including contact lenses, is described in U.S. Pat. No. 3,621,079.
U.S. Pat. No. 3,639,524 discloses the graft or block copolymerization of polyvinyl pyrrolidone with N-vinyl pyrrolidone and a monomeric methacrylate, optionally in the presence of a crosslinking agent and a catalyst, to prepare a crosslinked xerogel which can be machined into contact lens replicas and swollen in water to form a hydrated contact lens.
U.S. Pat. No. 3,894,129 discloses the graft or block copolymerization of polyvinyl lactams with a hydroxyalkyl methacrylate monomer in the presence of a polymerization initiator at low temperatures and containing not more than 0.7% alkyl glycol dimethyacrylate crosslinker, followed by a post polymerization heat treatment in the manufacture of contact lenses. This patent stresses the exclusion of oxygen from the polymerization reaction mixture on the grounds that oxygen inhibits polymerization and can cause uneven degrees of polymerization and monomer vaporization.
U.S. Pat. No. 4,138,408 discloses the graft or block copolymerization of a polyvinyl lactam with a mixture of hydrophilic and hydrophobic polymerizable monomers and a divinyl benzene or divinyltoluene crosslinking agent in the manufacture of contact lenses.
Unfortunately, due to the incomplete incorporation of polyvinyl lactam into the polymer network, such graft or block copolymers of the prior art, upon swelling with an aqueous medium, characteristically exhibit a relatively high degree of water soluble extractibles, comprising polyvinyl lactam containing residual products. Over a period of time, the mechanical properties of contact lenses made of such materials can degrade. Moreover, tinted lenses containing such extractibles can fade over an extended period of time.
It is thus an object of the present invention to provide an improved modified poly-N-vinyl lactams of increased reactivity with hydrophobic and hydrophilic monomers, and copolymers resulting therefrom.
It is a further object of the invention to provide crosslinked copolymers with a significantly reduced degree of extractibles.
These and other objects of the invention are apparent from the following disclosures.